Molybdenite widely spreads in the different types of ores from the Jiama copper polymetallic deposit. Skarn is the major host rock, then hornfel is the secondary, and porphyry, marble and limestone contain few molybdenite. Molybdenite samples with different occurrences from skarn, hornfel and porphyry were collected and tested by Re-Os isotopic dating. Mode age of 27 samples changed between 14.2 and 17.5 Ma and the isochron age was 15.22±0.59 Ma. The isochron ages of porphyry and hornfel were 14.78±0.33 Ma and 14.67±0.19 Ma, which were consistent to metallogenic period of other porphyry copper deposits in the Gangdese metallogenic belt. The 187Re content in molybdenite was correspondingly higher in the range of 38.75~387.4 g/g. Molybdenite in the Jiama ore deposit was supposed to form in one period occurring in the different rocks. It was in the Langhian Stage of Miocene with the feature of postcollision. The metallogenic period of the Jiama ore deposit was close to that of molybdenite, therefore the previous overview of effusive sedimentary metallogeny was not scientific.